Collapsible strut



Jan. 25, 1938. J. F. WALLACE 2,106,239

QCOLLAPSIBLE STRUT Filed Jan. 50, 1955 3 Sheets-Sheet 1 Y INVENTOR.

BY Mimi ATTORNEYS Jan. 25, 1938. J, WALLACE 2,106,289

COLLAPSIBLE STRUT Filed Jan. 30, 1935 3 Sheets-Sheet 2 Jan. 25, 1938. J.F. WALLACE 2,106,239

. COLLAPSIBLE STRUT Filed Jan. so, 1935 s Sheets-Shet s 7 INVENTOR.

ATTORNEYS Patented Jan. 25, 193s COLLAPSIBLE STRUT John F. Wallace,Cleveland, Ohio, alllgnor to The Cleveland Pneumatic Tool Company,Cleveland, Ohio, a corporation of Ohio Application January so, 1935,Serial No. 4.105

9 Claims.

This invention relates to improvements in collapsible struts, that is tosay struts having shock absorbing functions and used in the running gearof airplanes.

It is becoming increasingly the practice to retract the running gear ofan airplane after the latter is in the air in order tocut down windresistance. Sometimes the shock absorbing struts are so long as to makeit diflicult or inconvenient to provide pockets for them in the fuselageor wing structure. Sometimes also the design of a plane calls fornon-retractible struts longer than the needed length of the shockabsorber, in order to provide'suflicient ground clearance upon landing.In such cases it would be desirable to reduce the over-all length of thestruts after the plane is in flight. With these conditions in mind, theprincipal objects of my invention are:

The provision of airplane running gear wherein the shock absorbingstruts may be shortened or collapsed after the plane is in flight.

The provision of airplane running gear wherein the shock absorbingstruts may be shortened or collapsed and then folded or swung intopockets in the airplane not large enough to hold the struts in theirnon-collapsed condition.

The provision of means controllable from the cockpit of an airplane forcollapsing the shock absorbers before retracting them, and for puttingthem into operative condition again when they have been lowered intooperative position prior to landing.

The provision of shock absorbing struts of special design adapted foruse under the conditions named.

Other objects and features of novelty will appear as I proceed with thedescription of those embodiments of the invention which, for thepurposes of the present application, I have illustrated in theaccompanying drawings, in which Fig. 1 is a front elevational view of anairplane provided-with running gear embodying the present invention.

Fig. 2 is a diagrammatic view showing in elevation and vertical sectionone extensible and retractible strut of an airplane running gear,together with liquid connections and apparatus for contracting the strutor permitting its extension.

Figs. 3 and 4 are detail views showing the valve of Fig. 2 in diiierentpositions.

.Fig. 5 is a view similar to Fig. 2, showing an air system forretracting and expanding the strut.

Figs. 6 and 7 are detail views showing the valve of Fig. 5 in differentpositions.

Fig. 8 is a view similar to Figs. 2 and 5, but showing a strut capableof a double extension or contraction, and embodying in its control 5both compressed air and liquid.

Figs. 9 and 10 are detail views showing the air valve of Fig. 8 indifferent positions.

Figs. 11 and 12 are detail views showing the liquid valve of Fig. 8 indifferent positions.

Fig. 13 is an elevatlonal view partly broken away to show some of theelements in vertical section, illustrating a hydro-pneumatic shockabsorber which may be employed in connection with the invention, and

Fig. 14 is a similar view of a different form of shock absorber.

Referring first to the constructions shown in Figs. 2, 3 and 4, I 5 isan upper cylinder closed at its upper end by a head or cap 16 which is20 provided with an upwardly extending ear l1 having a pivot opening ittherein by means of which the strut or shock absorber may be mountedupon an airplane, as indicated in Fig.- 1, so as to be swung fromoperative or full line position to, inoperative or dotted llneposition.Telescoping with the cylinder I! there is a lower cylinder iii of adiameter small enough to be spaced inwardly from the cylinder l5, andprovided at its upper extremity with a piston 20 which slides on theinner wall of cylinder 15. At the lower end 'of cylinder l5 there is apacking 2i bearing on the outer surface of cylinder l9, and retained inplace by a gland ring 22. On the lower extremity of the cylinder l9there is mounted a wheel fork 23 carrying the spindle of ground wheel24. The fully extended position of the wheel is illustrated in fulllines, and the contracted position in dash lines.

The shock absorber of Fig. 2 is illustrated 40 rather diagrammatically,but one of similar construction and operation is shown more in detail inFig. 13. Referring to that figure, it will be observed that the piston20 has a central opening 25 through which projects a tubular rod 26, thelatter being securely mounted at its upper end in the head or cap 16ofthe cylinder IS. A plug 21 is set into the lower end of rod 26, andupon this plug there is threaded a disk 28 which has an easy sliding fitwithin cylinder I9. The disk 28 is held in place by a nut 29. Above thedisk 28 on a smooth part of the plug 21 there is slidably mounted anannular valve piece 30-, which is provided with one or more'restrictedopenings 3|. In the upper surface of disk 28 there is a circular groove32, and one or more holes 33 are drilled through the disk in such manneras to communicate with the groove 32.

The piston 28 has a skirt portion 34 which may be threaded exteriorly tothe cylinder I8, and is provided with a lower shouldered portion 35.Packing of suitable character is interposed between the skirt portion 34of the piston and the wall of cylinder 15. As illustrated herein it mayconsist of a cup leather 36, a thin metal ring 31, an annular packingring 38 of U-shaped cross section, a metal ring 39 having a dependingrib ,extending into the groove of the packing ring 38, a packing ring 48which is substantially the same as packing ring 38, and a metal ring 4|with an annular rib extending'into the groove of packing ring 48, thering 4| being threaded ontothe piston 28 and by adjustment serving tocompress the packing to the degree desired. The ring 4| may have holes42 therein serving both as spanner wrench holes and as holes foradmitting oil into the space below the ring 4|, which oil being underpressure and acting upon the beveled surfaces of the upper edge of ring48 tends to force and hold the upper edges of that ring against thesurfaces of the piston head 28 and cylinder I5.

In the lower end of the cylinder l5 there is threaded the ring 43.Between this ring and the cylinder i8 I mount packing of any suitablecharacter, and this packing is compressed to the required extent by agland ring 45. The lower end of cylinder I8 is closedand sealed by anysuitable cap or plug, as for instance by the plug 45 having a pair ofperforated ears 41, to which may be attached an axle or other means formounting a ground wheel, skid or the like. As to this detail ofconstruction a somewhat diiferent form is illustrated in Figs. 2 and 5.The cylinder I5 is an air cylinder, and is provided with a threadedopening 48 in which there may be mounted the usual air valve, or ifdesired a nipple may be mounted in this opening for connection with anair hose or tube 49. An air valve in a similar location is indicated at58 in Fig. 2. Cylinder I9 is filled with oil or other liquid, the liquidpreferably extending upwardly a short distance above the piston 28 intocylinder IS.

A hose or other tubular conductor 5| is connected into ring 43, andcommunicates with a passage 52 in that ring, whereby liquid may bereceived from the conductor 5| into the space below the annularshouldered portion 35 of the piston 28, the packing in the piston, andparticularly the cup leather 35, serving to prevent the leakage ofliquid upwardly out of the annular chamber surrounding the cylinder l8below the pistonhead.

When the air in the air cylinder I5 is exhausted or the pressure thereindissipated, oil or other liquid may be forced through conductor 5i intothe annular chamber beneath the piston which, with the cylinder 19, willthereby be forced upwardly to collapse the shock absorber and decreaseits length materially.

In the operation of this shock absorber any shock or impact delivered tocylinder l8 causes the latter to rise against the air cushion incylinder l5, by which the shock is absorbed or cushioned. During thisimpact stroke oil is forced upwardly through the openings 33, liftingvalve piece 38, as indicated in Fig. 13. Sufiicient clearance isprovided between the tubular rod 26 and the opening 25 in piston 28 topermit the oil displaced by the increasing length of rod 28 within thecylinder l8 to be forced into the cylinder l5. On the rebound the valvepiece 38 immediately seats itself, cutting oil free admission topassages 33 and necessitating the metering of oil through the restrictedpassage or passages 3|, thereby checking the rebound stroke.

Now referring again to Fig. 2, 53 is a storage tank for oil or otherliquid, the tank being located in some convenientpositionin theairplane. From this tank a conductor 54 extends to a hydraulic pump 55.From this pump another conductor 56 leads to a three-way valve 51. Fromthis waive a conductor 58 extends to the conductor 5|, which is joinedto the strut illustrated in Fig. 2 and also-to the similarly arrangedstrut on the opposite side of the fuselage. A further conductor v 58connects the valve with the tank and constitutes a return line.

It is to be understood that the air cylinder I5 is inflated by air underpressure introduced through the valve 58. The normal-position of valve51 is that illustrated in Fig. 4, whereby the conductors 58 and 5| arecut off from the pump 55 and from the tank 53. Now, when the airplanetakes off, the air pressure immediately extends the strut to thecondition illustrated by full lines in Fig. 2. The pilot may then turnthe valve 51 to the position illustrated in Fig. 2 and operate the pump55, drawing liquid from the tank 53 and forcing it through valve 51andconductors 58 and 5i to the two struts below the pistons 28 thereof. Thepistons will thereby be forced upwardly, compressing the air in the aircylinders IS. The pumping is continued until the cylinder I! is drawn upinto the cylinder l5 as far as it will go. Valve 51 is then turned totheposition of Fig. 4. The pilot then operates any suitable controls toswing the struts l5, IS on their pivots to retract the same with theground wheels into inoperative position, as illustrated for instance indotted lines in Fig. 1. Obviously the conductor 5i must be flexible, atleast in part.

Now, when a landing is to be made, the pilot by operating suitablecontrols known in the art will swing thestruts l5, l9 back to theirvertical or substantially vertical positions. He will then turn valve 51to the position illustrated in Fig. 3. whereby the heavy pressure in aircylinder l5 will become effective to force the piston 28 and piston rodl9 downwardly, causing the liquid in the annular chambers around thepiston rods l9 to be forced through conductors 5i and 58, through valve51, aridthence through conductor 59 back to tank 53. As soon as thismovement is completed, that is when the pistons 28 have descended as faras they can go the valve 51 is again turned to the position of Fig. 4.The oil lines 5| and 58 will then be filled with oil, and the action ofthe shock absorber will be the same as though there were no suchconnections.

In Fig. 5 I have illustrated another form of the invention, wherein theshock absorber itself may be nearly identical with that of Fig. 2, withpossibly some variation in the packing around the piston head, and withthe use of the air conductor 49 instead of the air valve 58. In thiscase air pressure is used to collapse the strut. An air tank 58 ismounted in the airplane in a convenient position. It is designed to holdair under pressure furnished throu a conductor from an ir compressor ofany suitable character driven by any suitable means. From the air tank aconductor 62 leads to a four-way valve Fmm this valve there is aconductor 84 which is connected with the conductor 5|, previouslyreferred to. The valve has a port 65 open to atmosphere,

-and also is connected by a conductor 65 with the conductor 49 which isconnected with the struts on both sides of the machine,'and must beflexible at least in part.

The normal position of valve 63 is the completely closed positionillustrated in Fig. 7. When the airplane takes ofi and is in flight, thepilot turns valve 63 to the position illustrated in Fig. 6, whereuponthe air chambers in the two cylinders l5 are connected to atmospherethrough conductors 49 and 55 and through valve 64 and open port 85. Atthe same time 'air tank 50 is connected through conductor 62, valve 65and conductors 64 and 5! with the annular chambers surrounding thepiston rods I! under pistons 2!). The pistons and piston rods arethereby forced upwardly to the limits of their movement, when the valve63 is again turned to closedposition, as in Fig. 7, thereby sealing theair pressure in the struts beneath the pistons and holding them in theelevated positions. The struts can then be swung into the dotted linepositions of Fig. 1.

When a landing is to be made the struts are lowered to their uprightpositions, and the pilot turns valve 53 to the position illustrated inFig. 5, whereupon the annular chambers beneath the pistons in the twostruts are vented to atmosphere through conductors 5| and 64, valve 63,and open port 65. At the same time air pressure is delivered to theupper air chambers in both struts from air tank 60 through conductor 62,valve 63. conductor 66 and conductor 49. The inflation of the airchambers continues until the desired pressure is obtained. The pressurecan be tested by turning the valve 63 to closed position and noting thereading on a pressure gauge 6'! in the conductor 49. When the desiredinflation is completed the valve 53 is turned to closed position, asindi cated in Fig. ,7, and the struts will then be in condition forlanding or taxiing.

In connection with the form of the invention illustrated in Fig. 8, astrut capable of double expansion and double contraction is employed. Anexample of such a strut is illustrated in Fig. 14, where the uppercylinder is shown at 68. This cylinder-near its lower end is providedwith a packing 58 which is held in place and in suitable compression bya gland nut III, the latter being formed at the upper end of a sleeve IIwhich in effect constitutes an extension of cylinder 68, although it isof smaller diameter than that cylinder.

Within the cylinder 88 there is slidably mounted a piston 12 threadedinto the upper end of ,a tubular piston rod 13. The lower part of thisthere is welded or otherwise secured a depending cylindrical member 15in the lower end of which is mounted a packing 11 held in place by glandnut 18. The cylinder 16 is therefore an extension of the tubular pistonrod I3, although the plug 14 cuts off any communication between them.

Within the cylinder 16 I mount a piston 19 and a tubular piston rod 80.The movements of these elements with respect to the cylinder 15 have noshock absorbing functions, but by means of such relative movement theeffective length of the strut may be changed, that is increased for op-,eration and shortened for flight.

The piston I5, it will be observed, is provided with a pair ofoppositely extending cup leathers ll and 02 separated by a metal ring 83which is threaded onto the tubular rod 80. 84 isa sleeve mounted on thetubular rod 80, the lower end of which is adapted, when this part of thestrut is expanded, to engage a' slidable metal ring 85 contacting withthe upper end of packing I1. When the sleeve 84 is pressed against thering 85 with'considerable force the packing I1 is thereby compressedlongitudinally and expanded trans versely, thereby more effectivelysealing the joint and preventing more certainly the leakage of oil.

A nipple 86 extends through a hole in cylinder 16 and is threaded intoan aligned hole in the depending skirt 15 of plug 14. To this nipple anoil conductor pipe 81 is connected. A nipple 88 is mounted in thereenforced lower end or cylinder l4 and has connected therewith an oilcondoctor 89. Obviously, when oil is forced into the.

- downwardly and the length of the strut accordingly increased; on theother hand, when oil in the upper end of the cylinder is free to exhaustand oil is forced into the lower end through conductor 89, the pistonwill be raised and the strut will be shortened. The lower end 90 ofpiston rod 80 is threaded for connection with a suitable mounting for awheel or skid. For example, the wheel fork 23 may be threaded into thislower en The shock absorber preferably comprises means for checkingrebound, which in this case may comprise an annular oil chamber9i,,passages 92 leading from the chamber to the uppersurface of thepiston head I2, and a ring valvei93 slidable upon the piston head.Clearance is provided between the periphery of this ring valve and thecylinderwall to permit rapid flow of oil into the chamber on the impactstroke. The ring has one or more constricted openings 94 therein,through which oil must be metered when the flow is out of the chamber 9|on the rebound stroke. By this means the rebound is checked,

' as will be apparent to those skilled in the art.

In the upper'end of cylinder 58 there is mounted a nipple 95 to whichis, connected a conductor 96 for the admission and discharge ofcompressed air.

Assuming that the strut is expanded, that is by oil in the cylinder 16above the piston head IS, the latter being at the bottom of its possibletravel, and assuming thata shock of impact is delivered to the lower endof piston rod80, the force of. that shock will then be transmitted tothe non-compressible liquid above the piston 19 and thence to the plug14 and the tubular piston rod IS. The compressed air in cylinder 68 willyield, and all of the'parts80, 19, I4, 13 and 12 will travel upwardly,further compressing the air in cylinder 58. The impact will thereby becushioned. As soon as the'upward stroke is brought to a stop positionbythe increased pressure in cylinder 68, the air begins to expand and thepiston 12 is forced downwardly; At this time however the annular chamberQi is full of oil which has no path oi exit except through theconstricted opening or openings 94, and consequently the rebound strokeis checked. During both 'ofthese movements of the tubular rod 93, thenipple 86 must move also. In order tojpermit suchmcvement a slot 91 isformed in the cylinder, 9| The conductors 95, 81 and 89 must of coursebe flexible, or include flexible portions.

Referring now to Fig. 8, it will be noted that any suitable .aircompressor.

there are some differences between the strut there illustrated and thatin Fig. 14, just described, but the functions of the two struts are thesame, and their connections with the air and oil conductors 96, 91 and99 are similarly arranged. In Fig. 8 I have shown a compressed air tank99, to which the conductor 96 is connected through a valve 99. The tankalso has a connection I99 leading to A conductor |9I branching fromconductor 96 is connected with the air chamber of the shock absorber onthe opposite side of the airplane at a point corresponding with that ofthe connection of coriductor 96 herein illustrated. The valve 99 has aport I92 leading to atmosphere. Normally the valve 99 will occupy'thepositionillustrated in Fig. 10, whereby all flow of air is cut oif. Whenit is desired to inflate the air chambers of the two struts, the valveis turned to the position of Fig. 8, the flow of compressed air takingplace from tank 99 through valve 99 and conductors 96'and I9I. When theair pressure in the two cylinders 69 is to be dissipated however,preparatory to contracting the strut, the valve 99 is turned to theposition illustrated in Fig. 9, at which time the air tank connection iscut off and the conductors 96 and IM are connected with atmospherethrough port I92.

A suitable tank for oil is shown at I93, con-' 'nected by a conductorI94 with a liquid pump I95,

which in turn is connected by a conductor I99 with a four-way valve I91.There is also a conductor I99 leading from the tank to the valve.Conductor 91 joins the two struts of the airplane at correspondingpoints. This conductor is in turn connected by a conductor I 99 withvalve I91. Conductor 99 also joins corresponding parts of the twostruts, and is connected by a conductor II9 with valve I91 as shown.

The normal position of valve I91 is that illustrated in Fig. 12, whereall four conductors are cut off from each other. When it is desired tocontract the strut, as when the plane is in flight, the pilot turnsvalve I91 to the position illustrated in Fig. 11. Oil is then free toflow from the upper end of cylinder 16 and the upper end of thecorresponding cylinder on the other side of the plane, throughconductors 91 and I 99 to valve I91 and out through conductor I99 backto oil tank I93. The pilot then causes pump I95 to be operated, drawingoil from tank I 99 through conductor I94 and forcing it throughconductor I96, valve I91, conductors H9 and 99 into the two cylinders 16beneath the pistons 19 outside of the tubular rods 99. The pistons 19and their rods 99 are thereby caused to rise, and this operation may becontinued until the piston has risen to the limit of its motion, whenthe pilot turns the valve I91 to the position of Fig. 12.

Now, when it is desired to expand thestrut again preparatory to landing,the'valve I 91 is turned to the position of Fig. 8 and the pump I95operated. Oil will then be drawn from the oil tank and pumped throughthe valve and conductors I99 and 91 to the upper ends of cylinders 19while oil is exhausted from the lower ends of those cylinders throughconductors 99 and H9, valve I91 and conductors I99 back to tank I93.

If it is desired to make use of the double contraction of the strut, thepistons 19 and piston rods 99 are raised by the oil system justdescribed, and the air is exhausted from air cylinder 69 as previouslydescribed. Then the pilot operates a winch II I mounted in the cockpitto wind up two cables or the like I I2 and H9 connected at their outer:extremities'with the respective wheel forks 29, thereby pulling upwardlyon the piston rod 99, from which effort is transmitted to plug 14 andthence to tubular rod 13. The latter with its piston 12 is therebylifted to the upper limit of its motion, accomplishing the doublecontraction of the strut. Thereafter the struts may be swung up intopockets in the airplane in any known manner it desir Having thusdescribed my invention, I claim:

1. In an airplane, a pair of hydro-pneumatic shock absorbers pivotallymounted at their upper ends, a ground engaging member mounted on thelower end of each shock absorber and carried thereby exclusively, meanscontrollable from the cockpit of the airplane for contracting the shockabsorbers, and means for swinging the contracted shock absorbers upontheir pivots in planes normal to the pivots through approximately aright angle into inoperative position.

2. In an airplane, a pair of fluid shock absorbers pivotally mounted attheir upper ends upon the airplane, a ground engaging member mounted Ion the lower end of each shock absorber and carried thereby exclusively,each shock absorber having pneumatic means adapted to cushion shocks ofimpact and liquid metering means adapted to check rebound, said shockabsorber having a chamber entirely separate from said shock absorbingand rebound checking means adapted when expanded to contract the shockabsorber, means controllable from the cockpit of the airplane forinjecting liquid into said chamber, and means for swinging thecontracted shock absorbers upon their pivots into inoperative position.

3. In an airplane, running gear comprising a shock absorber containing.an air cylinder, a piston movable therein, a piston rod for said piston,

said shock absorber having an annular chamber surroimding the piston rodclosed at one end by the piston and at the other end by the cylinder,and means operable from the cockpit of the plane for forcingincompressible fluid into said annular chamber for imparting movement tothe piston inwardly with respect to the said air cylinder andcompressing the air in said air cylinder, whereby the strut iscollapsed, and for withdrawing incompressible fluid from said annularchamber, whereby the air is again free to expand the shock absorber tooperative position.

4. In a fluid shock absorber, a pair of telescoping cylinders eachclosed at its outer end, means within said telescoping cylinders forabsorbing shocks of impact and rebound and an extension for one of saidtelescoping cylinders comprising a cylinder, piston and piston rod, andmeans for pumping liquid into said last named cylinder above or belowsaid piston, whereby the length of the said extension maybe varied.

5. In an airplane, a shock absorbing strut hingedly mounted at its upperend, a ground wheel mounted solely upon the lower end of the strut, andmeans operable from the cockpit of the plane for contracting said strut,said airplane having a pocket therein adapted to receive the wheel afterthe strut has been contracted and is swung upwardly on its hingemountnig.

6. In combination, a hydro-pneumatic shock absorber comprising an airchamber in which air takes shocks of impact and a liquid chamber fromwhich liquid is metered to check rebound, and a third chamber out ofcommunication with both of said first named chambers and unaffected bythe action of the fluid in said first named chambers, said shockabsorber being adapted to be contracted upon the expansion of said thirdchamber and to be extended upon the contraction of said third chamber.

'7. In an airplane, running gear comprising 5 shock absorbers mounted attheir upper ends on hinge pins extending longitudinally of the airplane.the mounting of the shock absorbers being otherwise immovable, groundwheels carried by the lower ends of the shock absorbers, means 10operable from the cockpit of the plane for contracting or expanding said"shock absorbers, and means operable from the cockpit of the plane forswinging the running gear about said hinge mountings after the shockabsorbers have been 15 contracted.

8. In an airplane, a pair offluid shock absorbers, a ground engagingmember mounted on the lower end or each shock absorber, each shockabsorber comprising a fluid cylinder and a piston 20 movable therein,each shock absorber comprising also a further cylinder and piston, andmeans controllable from the cockpit of the airplane for forcingincompressible fluid into said last named cylinder to one side of thepiston and exhausting it from the other, whereby the length of the shockabsorber may be varied without affecting the shock absorbing action.

9. In an airplane, running gear comprising shock absorbers hingedlymounted at their upper ends, said shock absorbers occupying anapproximately vertical operative position, ground wheels carriedexclusively by the lower ends of said shock absorbers, means operablefrom the cockpit of the airplane for expanding or contracting said shockabsorbers, and means operable from the

